The design and testing of a radio wave antenna has historically been principally concerned with the antenna's performance (especially gain) in the direction of its boresight or main beam axis. For this purpose, as diagrammatically illustrated in FIG. 1, an antenna 10 whose performance is to be measured may be mounted inside a compact test range 12, such as an EMI-shielded anechoic chamber, that is configured to eliminate reflections and interference from unwanted sources of electromagnetic radiation. Testing the antenna typically involves directing radio wave emissions from a test signal source 14 toward the antenna 10, and measuring the amplitude and phase response of the antenna by means of a range receiver 16, the output of which may be displayed or recorded via an associated test and measurement workstation 18. As the relative orthogonal principle planes (e.g., azimuth and elevation) parameters between the antenna 10 and test signal source 14 are varied (for example, by moving either the antenna or the test source), both boresight and off-axis gain parameters are derived.
Unfortunately, at relatively low frequencies, such as UHF, the size of such a test range becomes physically and cost-wise prohibitive, making it necessary to test the antenna design outdoors. While finding a location to set up an outdoor antenna test range that is free of interferers may not have been particularly difficult several decades ago, it has now become a significant problem due to the proliferation of wireless commercial products, such as cellular phones and citizen band radios, as well as specular reflections from buildings and the like.
Moreover, this interference and reflection free test range problem is compounded by the fact that antenna designers are no longer necessarily principally interested in boresight performance; they now must measure the antenna's off-axis characteristics, in order, for example, to evaluate its ability to place nulls on one or more of the continually growing number of interferers,.such as the cellular phone and CB radio devices, referenced above. Thus, the outdoor test range operator could face the dilemma of trying to measure side lobe characteristics of the antenna, without the presence of one or more likely interferers, while at the same time designing the antenna to exhibit a characteristic that allows placement of nulls on such interferers.